Beschrijving:USAir Flight 224 departed Philadelphia on a scheduled flight to Boston. While climbing through 4000 feet, the aircraft yawed and rolled to the right. Simultaneously, the crew noticed the nr. 2 throttle slam and lock to the idle position. A continuous airframe buffet began. Soon thereafter, the nr. 2 engine separated from the aircraft and the buffet stopped. The engine impacted in an open field, 6 miles from the airport. After separation, the 'B' hydraulic system lost pressure and the flaps would only extend to 10 deg. The aircraft was landed safely after an emergency gear extension and differential braking was used for steering. It appeared that the aft mount cone bolt for the nr. 2 engine had failed from fatigue through the thread relief undercut radius. Fatigue cracks had initiated on diametrically opposite sides of the radius. Subsequently, the forward mount cone bolts and secondary support cable failed from overload.

PROBABLE CAUSE: "Previous damage to the aft cone (engine mounting) bolt, which resulted in mismatched surfaces between the bolt and isolation mount, loss of torque during cyclic loading of the mounting bolt, and subsequent fatigue failure of the bolt."

Bronnen:

» Aviation Week & Space Technology 30 Jan. 1989 (p.71)» NTSB

Veiligheidsmaatregelen

NTSB issued 2 Safety Recommendations

Issued: 21-DEC-1987

To: FAA

A-87-125

ISSUE AN AIRWORTHINESS DIRECTIVE REQUIRING OPERATORS OF BOEING 737-100 AND -200 AIRPLANES WITH ENGINE AFT MOUNT SUPPORT CABLES TO CHECK FOR ENGINE SECURITY BY PERFORMING A "RED STRIPE INSPECTION" BEFORE EACH FLIGHT TO VERIFY THAT THE AFT CONE ATTACHMENT BOLT IS INTACT ON EACH ENGINE. (Closed - Acceptable Alternate Action)

Issued: 21-DEC-1987

To: FAA

A-87-126

ISSUE AN AIRWORTHINESS DIRECTIVE REQUIRING OPERATORS OF BOEING 737-100 AND -200 AIRPLANES TO PERIODICALLY INSPECT THE THREAD RELIEF UNDERCUT RADIUS OF THE AFT CONE ATTACHMENT BOLT OF EACH ENGINE FOR EVIDENCE OF CRACKING; SUCH INSPECTIONS SHOULD BE AT SERVICE TIME INTERVALS THAT WILL ENSURE THAT A FATIGUE CRACK IN THE BOLT WILL NOT PROPAGATE TO A CRITICAL CRACK LENGTH BEFORE DETECTION. (Closed - Acceptable Action)

This information is not presented as the Flight Safety Foundation or the Aviation Safety Networkĺs opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.